An aged and wrinkled face drawn by Leonardo da Vinci, widely considered a self-portrait, is in danger of fading away. Using a new, harmless method to assess chemical damage of the red chalk drawing, researchers found significant decay in the cellulose fibers of the paper. Such damage leads to the characteristic yellowing of timeworn paper.

The method, developed by physicist Adriano Mosca Conte of the University of Tor Vergata in Rome and colleagues, uses the spectrum of light that bounces off ...